The present disclosure generally relates to a method for preparing 1,1,1-tris(4-hydroxyphenyl)alkanes.
The 1,1,1-tris(4-hydroxyphenyl)alkanes, such as, for example, those disclosed in U.S. Pat. Nos. 3,579,542 and 4,992,598, can be used as branching agents during the polymerization of polycarbonates. As such, it may be incorporated into reaction mixtures containing dihydroxy aromatic compounds such as bisphenol A and carbonate sources such as phosgene or diphenyl carbonate, among others.
An exemplary 1,1,1-tris(4-hydroxyphenyl)alkane, 1,1,1,-tris(4-hydroxphenyl)ethane (also referred to as THPE), can generally be prepared by the reaction of 4-hydroxyacetophenone with phenol. The reaction is analogous to the well known reaction of phenol with acetone to form 2,2-bis(4-hydroxyphenyl)propane (also commonly referred to as “bisphenol A”). U.S. Pat. No. 5,756,781 discloses reacting “phenol and 4-hydroyxacetophenone” in the presence of effective amounts of an ion exchange catalyst and a mercaptan as a co-promoter such that the resulting 1,1,1-tris(4′-hydroxyphenyl)ethane is substantially free of various reaction impurities.
U.S. Pat. No. 5,756,859 discloses reacting “phenol and 2,4-pentanedione under acidic conditions and in the presence of an effective amount of mercapto compound as promoter.” This patent further states that “[t]he acidic conditions may be provided by the addition of any acidic material, especially a relatively volatile material such as hydrogen chloride.” The patent next states that “[t]ypically, hydrogen chloride gas is passed through the mixture during the reaction.”
Among the disadvantages to this method are that the quantity of catalyst used is relatively high and the volatile acids employed, e.g., hydrogen chloride gas, are generally corrosive. Other methods include the use of sulfuric acid in conjunction with 3-mercaptosulfonic acid as the promoter.
Accordingly, there remains a need in the art of efficient methods for preparing 1,1,1-tris(4-hydroxyphenyl)alkanes in high yields.